Kapteyn's Star
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation | Pictor |
| Right ascension | 05h 11m 40.6s |
| Declination | -45° 01' 06" |
| Apparent magnitude (V) | 8.85 |
| Spectral Characteristics | |
| Spectral type | sdM1 V |
| U-B color index | 1.15 |
| B-V color index | 1.56 |
| Variable type | Unknown |
| Astrometry | |
| Radial velocity (Rv) | +245.5 km/s |
| Proper motion (μ) | RA: 6506.05 mas/yr Dec.: -5731.39 mas/yr |
| Parallax (π) | 255.27 ± 0.86 mas |
| Distance | 12.78 ± 0.04 ly (3.92 ± 0.01 pc) |
| Absolute magnitude (MV) | 10.88 |
| Physical Characteristics | |
| Mass | 0.38 M☉ |
| Radius | 0.24 R☉ |
| Luminosity | 0.004 L☉ |
| Temperature | 3,800 K |
| Metallicity | 32% |
| Rotation | |
| Age | ? years |
| Other designations | |
Kapteyn's Star (also known as GJ 191, HD 33793 or CD -45 1841) is a class M0 subdwarf discovered by Jacobus Kapteyn in 1897. It is 12.79 light years from Earth's Solar System, and is distinctive in a number of regards; it has a high radial velocity, orbits the Milky Way retrograde, and is the nearest halo star to the Sun.
When discovered, it had the highest proper motion of any star known, dethroning Groombridge 1830. Later it dropped to second place after the discovery of Barnard's Star.
